Power system inhibit method and device and structure therefor

ABSTRACT

A power control system ( 25 ) uses two separate currents to control a startup operation of the power control system ( 25 ). The two currents are shunted to ground to inhibit operation of the power control system ( 25 ) and one of the two currents is disabled to minimize power dissipation. The two independently controlled currents are generated by a multiple output current high voltage device ( 12 ) responsively to two separate control signals ( 23,24 ).

BACKGROUND OF THE INVENTION

The present invention relates, in general, to electronics, and moreparticularly, to methods of forming semiconductor devices and structure.

In the past, the electronics industry utilized various methods anddevices to control high value or large input voltages in order toprovide controlled output voltages and currents. One example of such adevice, referred to as an off-line bootstrap startup circuit, wasdisclosed in U.S. Pat. No. 5,477,175 issued to Tisinger et al on Dec.19, 1995 and which is hereby incorporated herein by reference. Thebootstrap startup circuit received a large input voltage and produced anoutput current that charged a capacitor and generated an output voltage.However, many applications required a sequence of currents that could becontrolled to charge the capacitor and form the output voltage. However,using multiple bootstrap startup circuits increased the manufacturingcost and complexity of the resulting semiconductor products and ofapplications using the products.

Accordingly, it is desirable to have a startup circuit that can receivean input voltage having a high voltage value and produce a sequence ofcurrents from the input voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an embodiment of a portion of a highvoltage multiple output current device in accordance with the presentinvention;

FIG. 2 illustrates an enlarged plan view of a portion of an embodimentof the high voltage multiple output current device of FIG. 1 inaccordance with the present invention;

FIG. 3 illustrates an enlarged cross-sectional view of a portion of thehigh voltage multiple output current device of FIG. 2 in accordance withthe present invention;

FIG. 4 schematically illustrates an embodiment of a portion of a powercontrol circuit that utilizes the high voltage multiple output currentdevice of FIG. 2 in accordance with the present invention;

FIG. 5 graphically illustrates some signals of the power control circuitof FIG. 4 in accordance with the present invention; and

FIG. 6 schematically illustrates an embodiment of a portion of anelectrostatic discharge (ESD) protection circuit that utilizes the highvoltage multiple output current device of FIG. 2 in accordance with thepresent invention.

For simplicity and clarity of illustration, elements in the figures arenot necessarily to scale, and the same reference numbers in differentfigures denote the same elements. Additionally, descriptions and detailsof well known steps and elements are omitted for simplicity of thedescription. As used herein current carrying electrode means an elementof a device that carries current through the device such as a source ora drain of an MOS transistor or an emitter or a collector of a bipolartransistor, and a control electrode means an element of the device thatcontrols current through the device such as a gate of an MOS transistoror a base of a bipolar transistor.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an embodiment of a portion of a highvoltage multiple output current device 12 that can generate multipleindependently controlled output currents from a single high voltageinput. Device 12 includes a high voltage multiple output element 11 thatpreferably is formed to include a JFET transistor 13, a first MOStransistor 14, and a second MOS transistor 15. Device 12 also includes afirst bias resistor 17 and a second bias resistor 18 that are formed toprovide bias currents to the gates of transistors 14 and 15,respectively. Device 12 is formed to receive a high voltage on a highvoltage input 22 and generate a first output current and a second outputcurrent on outputs 19 and 21, respectively, in response to controlsignals applied to control inputs 23 and 24, respectively.

In order to provide this functionality, a drain of transistor 13 isconnected to input 22 and a source is connected to a common node 16. Adrain of transistors 14 and 15 is connected to the source of transistor13 and to node 16. A gate of transistor 14 is connected to input 23 andto a first terminal of resistor 17, and a source is connected to output19. Transistor 15 has a gate connected to input 24 and to a firstterminal of resistor 18, and a source connected to output 21. A secondterminal of both resistors 17 and 18 is connected to the source oftransistor 13 and to the drains of transistors 14 and 15. The gateconnection of transistor 13 will be explained in more detail in thedescription of FIG. 3. In the preferred embodiment, transistors 14 and15 are both N-channel MOS transistors and transistor 13 is an N-channelJ-FET transistor. In other embodiments, transistors 14 and 15 may beother transistors structures such as J-FETs and bipolar transistors.

When voltage is applied to input 22, outputs 19 and 21 are controlled bythe voltages applied to control inputs 23 and 24. Transistors 14 and 15are independently enabled and disabled, thus, each respective output 19and 21 has independently controlled output currents. If no externalvoltage is applied to either input 23 or 24, for example input 23 or 24is floating, respective resistor 17 or 18 supplies a bias current fromtransistor 13 to enable device 12 and the respective transistor togenerate an output current at respective output 19 or 21. In anoperational circuit, a control voltage typically is applied to inputs 23and 24 to control the value of the output current. When the voltageapplied to input 23 or 24 produces a gate-to-source voltage that is lessthan the threshold voltage of the respective transistor, that transistortypically is disabled. Even when either of transistors 14 or 15 isdisabled, current still flows through respective resistor 17 or 18,thus, resistors 17 and 18 are designed to ensure that the bias currentis very small in order to minimize the power dissipation of device 12.Disabling both transistors 14 and 15 disables device 12. When thevoltage applied to input 23 produces a gate-to-source voltage that isgreater than the threshold voltage of transistor 14, transistor 14 isenabled and current flows through transistors 13 and 14 to output 19.Similarly, when the voltage applied to input 24 is greater than thethreshold voltage of transistor 15, transistors 13 and 15 are enabledand current flows through transistors 13 and 15 to output 21. As will beseen hereinafter, the novel construction of device 12 and element 11facilitates generating these two different and independently controlledoutput currents from one device. The maximum value of the outputcurrents supplied by device 12 is selected by adjusting the width of thechannel of transistors 14 and 15.

The breakdown voltages for transistors 13, 14, and 15 depend on theapplication and various other factors. In one embodiment for world wideline voltage applications, the breakdown voltage at the drain oftransistor 13 with respect to substrate 76 may exceed four hundred volts(400 V) and the sustainable voltage at the source of transistors 14 and15 may exceed fifty volts (50 V).

FIG. 2 illustrates an enlarged plan view of a portion of an embodimentof device 12 explained in the description of FIG. 1. FIG. 3 illustratesan enlarged cross-sectional view of device 12 illustrated in FIG. 2along section line 3-3. This description has references to both FIG. 2and FIG. 3. Transistors 14 and 15 are identified in general by dashedlines in FIG. 2. Transistors 13, 14, and 15 are formed as closedgeometric shapes on a surface of a semiconductor substrate 76. Typicallythe closed geometric shapes have centers that are concentric and havesome overlapping periphery. In the preferred embodiment, the closedgeometric shapes are formed as circles or arcs of circles having variousconcentric radii. For clarity of the explanation, the preferredembodiment is explained, however, those skilled in the art will realizethat other closed shapes such as ellipses, squares, pentagons, hexagons,etc. may also be used instead of circles and that transistors 13, 14,and 15 may have different lengths and widths.

In the preferred embodiment, the closed geometric shapes of transistor13 are formed as concentric circles that have increasing radii. A firstportion of the geometric shapes of transistors 14 and 15 are formed as acircle and a second portion are formed as arcs of a circle with the arcshaving radii that are larger than radii of the circle portion oftransistors 13, 14, and 15. Transistor 13 is formed to include a draincontact 72 and a drain electrode 71 that overlies contact 72. Transistor14 also includes a pair of doped regions shaped as arcs of a circle thatform a pair of source regions 84 and a gate polysilicon 88 shaped as anarc of a circle. Transistor 15 includes a pair of doped regions shapedas arcs of a circle that form a pair of source regions 85 and a gatepolysilicon 86 shaped as an arc of a circle.

In the preferred embodiment, drain contact 72 of transistor 13 is formedas a doped region on the surface of substrate 76. Contact 72 is shapedas a hollow first circle having a first radius and a center 70. Acircular shaped doped region 73 is formed on the surface of substrate 76concentric with contact 72 and with a second radius that is larger thanthe radius of contact 72. Because of the hollow circle shape of contact72, a first circular shaped inner portion of region 73 underlies contact72 (see FIG. 3). A second circular portion of region 73 extends from theouter circumference of contact 72 to an inner edge of polysilicon 88 and86, and forms the channel of transistor 13. The interface of substrate76 with the portion of region 73 underlying contact 72 and the secondportion of region 73 functions as the gate of J-FET transistor 13.Typically substrate 76, and thus the gate of transistor 13, is connectedto the lowest potential in the circuit that uses device 12. The arc ofregion 73 underlying the inner arc of polysilicon 88 and 86 forms thesource of transistor 13 and the drain of each of transistors 14 and 15,respectively. This third circular shaped region extends radially to anouter edge 77 of region 73. Thus the drain and source of transistor 13are formed as closed geometric shapes with the source having a radiusthat is larger than the drain. Also, one doped region is used to formthe source and drain of transistor 13 and the drain of transistors 14and 15.

Source regions 84 of transistor 14 are formed as two doped areas eachshaped as an arc of a circle having a larger radius then the radius ofthe drain of transistor 14. Typically, an inner portion of source region84 underlies polysilicon 88. Source contact 83 is formed within sourceregion 84. The two doped areas of source regions 84 are spaced apart byan opening 114 that is formed along the outer periphery of polysilicon88. A portion of polysilicon 88 extends through opening 114 and forms atab 116 that facilitates making contact to polysilicon 88. Resistor 17is formed as a doped region on the surface of substrate 76. One end ofresistor 17 extends under tab 116, illustrated by dashed lines, to makeelectrical contact to region 73 at node 16. A second end of resistor 17is connected to tab 116 by a metal connection 118. Similarly, sourceregions 85 of transistor 15 are formed as two doped areas each shaped asan arc having a radius larger than the radius of the drain of transistor15. Typically, an inner portion of source region 85 underliespolysilicon 86. Source contact 80 is formed within source region 85. Thetwo doped areas of source regions 85 are spaced apart by an opening 115that is formed along the outer periphery of polysilicon 86. A portion ofpolysilicon 86 extends through opening 115 and forms a tab 117 thatfacilitates making contact to polysilicon 86. Resistor 18 is formed as adoped region on the surface of substrate 76. One end of resistor 18extends under tab 117, illustrated by dashed lines, to make electricalcontact to region 73 at node 16. A second end of resistor 18 isconnected to tab 117 by a metal connection 119. Using two doped regionsfor the source of each of transistors 14 and 15 facilitates connectingto the gate electrode of each transistor and forming resistors 17 and18.

As can be seen from the explanation of FIGS. 2 and 3, an internalperiphery of the circle portion of transistors 14 and 15 formed byregion 73 merges into the external periphery of transistor 13 to form asource of transistor 13 that merges into the drain of transistors 14 and15. The outer periphery of region 73 has a curved contour and the innerperiphery of regions 84 and 85 have a shape that is the same as theshape of the periphery of region 73. Additionally, gate structures 78and 79 have a contour that is the same as the shape of the outerperiphery of region 73. Using the same contour facilities forming a wellcontrolled channel for transistors 14 and 15.

In the preferred embodiment, drain electrode 71 is formed as a closedcircle on an insulator 64, such as a field oxide and on an interlayerdielectric 102. Since drain contact 72 has the hollow circleconfiguration, a portion of electrode 71 overlying contact 72 extendsthrough insulator 64 and dielectric 102 to contact 72. Electrode 71 isalso formed to function as a bonding pad to make contact to device 12.The open section in the center portion of contact 72 facilitates bondingto electrode 71 without damaging device 12. In other embodiments,contact 72 can be formed as a closed circle within region 73.

Referring to FIG. 3, transistors 13, 14, and 15 are formed on thesurface of substrate 76. A portion of the surface of substrate 76 isdoped in order to form circular shape region 73. A portion of region 73is more heavily doped in order to form concentric hollow circular shapeddrain contact 72 within region 73. Source region 85 and source region 84are formed as doped regions on the surface of substrate 76 and spacedapart from the circumference of region 73. Source contacts 83 and 80 areformed in respective source regions 84 and 85.

A body region 75 of transistor 14 is formed as a doped region on thesurface of substrate 76 underlying polysilicon 88. A portion of region75 extends through opening 114 (FIG. 2) to facilitate forming contact toregion 75. Similarly, a body region 74 of transistor 15 is formed as adoped region on the surface of substrate 76 underlying polysilicon 86.For clarity of the drawings, the extension through openings 114 and 115is not shown. A portion of region 74 extends through opening 115 (FIG.2) to facilitate forming contact to region 74. A gate structure 78 isformed on substrate 76 interposed between source region 84 and region 73and a gate structure 79 is formed on substrate 76 interposed betweensource region 85 and region 73. Gate structure 78 includes a gateinsulator 81 formed on substrate 76, gate polysilicon 88 formed oninsulator 81 and dielectric 102 formed on polysilicon 88. Similarly,gate structure 79 includes a gate insulator 82 formed on substrate 76,gate polysilicon 86 formed on insulator 81, dielectric 102 formed onpolysilicon 86, and gate electrode 87 formed on dielectric 102.Typically, one edge of structure 78 overlies a portion of source region84 and another edge overlies a portion of region 73. Similarly, one edgeof structure 79 overlies a portion of source region 85 and another edgeoverlies a portion of region 73. Preferably substrate 76 is a P-typematerial, and region 73, source region 85, and source region 84, areN-type material resulting in transistor 13 being formed as an N-channelmode J-FET transistor and transistors 14 and 15 being formed asN-channel MOS transistors.

Those skilled in the art will realize that the closed geometry of thecircular shapes of device 12 may also be formed with region 73 formed asan ellipse and regions 84 and 85 formed as arcs, a square with regions84 and 85 formed as a rectangle along each side of the square, apentagon with regions 84 and 85 formed as a rectangle along some sidesof the pentagon, a hexagon with regions 84 and 85 formed as a rectanglealong some sides of the hexagon, etc.

FIG. 4 schematically illustrates an embodiment of a portion of a powercontrol system 25 that uses device 12. Power control system 25 usesdevice 12 and a startup control circuit 34 for controlling a highvoltage power-up sequence of system 25 and for inhibiting the operationof system 25. System 25 receives an input voltage between a voltageinput 57 and a voltage return 58. Other components typically areexternally connected to circuit 34 in order to provide the desiredfunctions of system 25. For example, an energy storage capacitor 49, atransformer 53 having a primary inductance 54, a secondary inductance 55and an auxiliary inductance 60, a rectifying diode 61, another storagecapacitor 62, a pulse width modulator (PWM) controller 51, a powertransistor 52, an inhibit transistor 35, and a load 63 typically are apart of system 25. Capacitors 49 and 62, transformer 53, controller 51,transistor 52, and diodes 61 and 30 are shown merely to assist indescribing the operation of device 12 and circuit 34. Those skilled inthe art understand that other well known components and functions thatare not shown in FIG. 4 typically are included to form a complete powercontrol system. In most embodiments, capacitors 49 and 62, transformer53, controller 51, transistor 35, and diodes 61 and 30 are external tothe semiconductor die on which device 12 and circuit 34 are formed. Insome embodiments, controller 51 or transistor 52 may be another portionof the semiconductor die on which device 12 and circuit 34 are formed ormay be external. In the preferred embodiment, transistor 14 has anarrower channel width than transistor 15 and provides a smaller outputcurrent on output 19 than transistor 15 provides on output 21. In thispreferred embodiment, transistor 15 is formed to have a width ofapproximately six hundred (600) microns and transistor 14 is formed tohave a width of approximately one hundred (100) microns. Those skilledin the art will realize that transistors 14 and 15 can be formed to haveapproximately equal widths or various other widths depending on therequired current density and transistor design rules.

Device 12 and circuit 34 are utilized to provide an initial voltage thatis used to power circuits within system 25 so that system 25 may providea smooth controlled startup of the initial voltage sequence that isapplied to other circuits connected to system 25, such as controller 51.Circuit 34 has a first output 46 and a second output 47 that provide twocontrolled currents that are essentially equal to the first outputcurrent from output 19 and the second output current from output 21 ofdevice 12. In the preferred embodiment, outputs 46 and 47 are connectedtogether to form an output 48 and an associated controlled outputcurrent of circuit 34. In other embodiments, outputs 46 and 47 may beseparated and used to provide current to different circuit functions. Inorder to control the output currents of device 12, circuit 34 has afirst current control loop that includes a first sense resistor 26, afirst sense transistor 28, and a first current mirror 31 that includes afirst reference transistor 32 and a first mirror transistor 33. A secondcurrent control loop of circuit 34 includes a second sense resistor 27,a second sense transistor 29, and a second current mirror 36 thatincludes a second reference transistor 37 and a second mirror transistor38. The first output current generated at output 19 is controlled by thefirst control loop. The current at output 19 flows through resistor 26and generates a corresponding voltage drop across resistor 26. Resistor26 is connected between the gate and source of transistor 28 and formsthe gate-to-source voltage of transistor 28, thus, the voltage dropacross resistor 26 establishes a first sense current flow throughtransistor 28. Current mirror 31 receives the first sense current fromtransistor 28 and responsively controls the voltage applied to controlinput 23 thereby controlling the gate voltage of transistor 14 and thevalue of the first output current. As the output current on output 19increases, the first sense current correspondingly increases andresponsively lowers the gate voltage of transistor 28 andcorrespondingly the control voltage on input 23 to reduce the outputcurrent value. This negative feedback loop, therefore, acts to regulatethe current in transistor 14. Similarly the second control loop includesa second bias resistor 27 coupled to receive the second output currentat output 21 and responsively generate a gate-to-source voltage fortransistor 29 and responsively generate a second sense current flowingthrough transistor 29. Transistor 29 is coupled to second current mirror36 which receives the second sense current from transistor 29 andresponsively controls the control voltage applied to second controlinput 24 thereby controlling the gate voltage of transistor 15 and thevalue of the second output current. The two current control loops may beomitted in some embodiments.

Circuit 34 also includes an operating voltage detector 39 and an initialvoltage detector 40 that are utilized to sequence the operation ofdevice 12. During the startup period, detectors 39 and 40 control theoperation of transistors 14 and 15 based on the value of the voltageformed at output 48. In some embodiments, outputs 46 and 47 may beseparated and used to provide current to different circuit functions,thus, detectors 39 and 40 may be connected to the same or differentoutputs of circuit 34 or other circuits (see for example FIG. 6). Avoltage reference 56 provides two reference voltages on a first andsecond output of reference 56. The two reference voltages are used bydetectors 39 and 40 to set the detection level for detecting the initialvoltage value and the desired operating voltage value. Controller 51 hasan enable input that is controlled by the output of detector 39 toensure that controller 51 does not drive primary inductance 54 until thedesired operating voltage is reached. Those skilled in the art willrealize that the current control loops and detectors 39 and 40 may beimplemented by a variety of designs as long as the control loop controlsthe current, and the detectors control device 12 based on the voltage onoutputs 46 and 47.

As the voltage at inputs 57 and 22 begins at zero and increases withrespect to time, the output voltage at outputs 46 and 47 begins at zeroand increases past an initial voltage value and reaches a desiredoperating voltage value. The desired operating voltage value typicallyis selected to be a value that provides normal operation for othercircuits external to circuit 34 such as controller 51 and load 63. Theinitial voltage value typically is much less than the desired operatingvalue and generally is a lower limit of voltage values that can beutilized to operate some basic circuit functions. For example, theinitial voltage value may be a value at which some basic comparators orother circuits need to operate prior to the output voltage reaching itsdesired operating value. The initial voltage value typically is used foroperating reference 56 and detectors 39 and 40. In order to provide thisinitial voltage, output 48 is connected to capacitor 49 and the currentfrom outputs 46 and 47 charges capacitor 49 to form an output voltage ofcircuit 34 on output 48. Circuit 34 receives this output voltage andresponsively controls the sequencing of device 12. The initial voltagevalue is selected to be as low as possible so capacitor 49 may becharged to the initial value as soon as possible in order to minimizethe amount of time required to startup system 25.

Detector 40 is formed to receive the output voltage and responsivelydisable transistor 15 and enable device 12 to supply current fromtransistor 14 as long as the output voltage is less than the initialvoltage value. When the output voltage is equal to or greater than theinitial voltage value, detector 40 also enables transistor 15 so thatdevice 12 can generate both the first and second output currents.Detector 39 is formed to receive the output voltage on output 48 andresponsively disable device 12 when the output voltage is equal to orgreater than the desired operating voltage value. In the preferredembodiment, detector 39 has hysteresis to prevent detector 39 fromswitching on and off as the output voltage varies slightly around thedesired operating voltage value. Due to the hysteresis input, detector39 re-enables device 12 when the output voltage decreases to a thirdvalue that is approximately equal to the desired operating voltage valueminus the hysteresis offset voltage of detector 39. To assist in thisfunction, detector 39 has an input coupled to output 48 and two outputsthat are respectively coupled to a first disable transistor 41 and asecond disable transistor 42. Each of detectors 39 and 40 and theassociated reference may be formed by a variety of circuits that arewell known to those skilled in the art including a single MOS transistorthat uses the transistor's threshold to establish the reference voltagevalue.

FIG. 5 is a graph having plots 43 and 45 that illustrate the outputvoltage and output current, respectively, of circuit 34. Thisdescription has references to both FIG. 4 and FIG. 5. Prior to applyingpower to input 57, capacitors 62 and 49 are discharged and output 48 isat zero volts. Consequently, circuit 34 is not operating and there is nooutput current from device 12. When an input voltage is applied to input57 at time To, current begins to flow through inductance 54 and intoinput 22 of device 12. As the voltage on input 22 increases, transistor13 turns-on and supplies a bias current through resistors 17 and 18 totransistors 14 and 15. The output of detector 39 is low and the outputof detector 40 is high, thus, transistors 41 and 42 are disabled andtransistor 44 is enabled to pull input 24 low and disable transistor 15.Resistor 17 pulls control input 23, thus the gate of transistor 14, tothe input voltage at input 22 and enables transistors 14 to supply thefirst output current to circuit 34. Circuit 34 controls the outputcurrent to supply the first control current to output 48 at an outputcurrent value 68 (See plot 45). The output current begins chargingcapacitor 49. At time T1, capacitor 49 has charged to initial voltagevalue 65 and the output of detector 40 switches to a low value therebydisabling transistor 44 and allowing resistor 18 to enable transistor15. Circuit 34 receives the second output current and controls the valueto provide the second control current to output 48. Circuit 34 alsoprovides a third output to controller 51. Transistor 14 remains enabled,consequently, the controlled output current at output 48 increases to avalue 69, and capacitor 49 is now charged by both the first and thesecond output currents from device 12. When the value of the voltage onoutput 48 increases to the desired operating voltage value 66 at timeT2, the output of detector 39 switches to a high value thereby enablingtransistors 41 and 42 to pull control inputs 23 and 24 low and disablingdevice 12. The high on the output of detector 39 also enables controller51 and transistor 52 begins to drive input 22 responsively to controller51. System 25 begins supplying power to load 63. If the output voltageon output 48 decreases to a third voltage value 67, the hysteresisoffset of detector 39 detects the low voltage at a time T3 and disablestransistors 41 and 42 thereby enabling device 12 to supply the first andsecond output currents to output 48 and once again charging capacitor 49to operating voltage value 66. Third voltage value 67 may be any valueincluding a value very near to value 65.

During the operation of system 25, it may be appropriate to disable orinhibit system 25. For example, load 63 may detect a condition thatrequires disabling system 25. In such a case, load 63 or another circuit(not shown) may enable transistor 35 to pull output 48 low and inhibitthe operation of system 25. Pulling output 48 low discharges capacitor49. When capacitor 49 is discharged to a value less than the initialvoltage value, detector 40 enables transistor 44 to disable transistor15 of device 12. Disabling transistor 15 inhibits system 25 fromsupplying the second output current and keeps device 12 enabled tosupply the first output current. Since the first output current is muchsmaller than the second output current, preferably at least ten timesless, keeping transistor 14 enabled disables controller 51 and preventssystem 25 from providing the voltage to load 63, and allows device 12 tosupply a the first output current as a standby current. Thus, thismethod provides an easy method to inhibit the operation of system 25while maintaining a standby current and provides a method that allowseasily recharging capacitor 49 when load 63 disables transistor 35. Itis important to minimize the amount of power dissipated while system 25is inhibited. Because of the low current of the first output current,this method of inhibiting system 25 minimizes the amount of powerdissipated from the voltage applied to input 57. Typically the value ofthe first output current is chosen to be less than the standby currentspecified in certification criteria such as ENERGY STAR®. It can be seenthat device 12 and transistor 35 form an inhibit circuit of systemcontroller 50 and system 25.

Those skilled in the art will understand that transistor 35 may beenabled at any time in the operational sequence and the inhibit functionbegins at the output voltage and current values existing at that time.Additionally, detectors 39 and 40 could also use other control sequencessuch as enabling device 12 to supply only the second output currentafter detecting the initial voltage value, or could reverse the sequenceand supply the second output current before detecting the initialvoltage value and supply the first output current after detecting theinitial voltage value, etc.

FIG. 6 schematically illustrates an embodiment of a portion of anelectro-static discharge (ESD) protection circuit 90. Circuit 90utilizes output 21 of device 12 as a startup current source to provide acontrolled startup voltage at output 91 and utilizes output 19 to alsoenable ESD protection for circuits connected to input 57. Often duringthe operation of an electrical circuit, the circuit may receive an ESDdischarge from an external source. Such an ESD discharge can easilydamage semiconductor devices that are connected close to the source ofthe ESD discharge. Circuit 90 utilizes transistor 14 of device 12 toenable transistor 97 during an ESD event and uses transistor 15 toprovide the controlled startup of the output voltage on an output 91 ofcircuit 90. Thus, transistors 14 and 15 operate independently toimplement two different functions that are derived from the output oftransistor 13. Detector 39 and transistor 41 are used to controltransistor 15 to provide the control startup of the output voltage, andan ESD detector 96 is used to disable transistor 14 unless an ESD eventoccurs. Circuit 90 also includes a reference 93 that provides a firstreference voltage that is used for detecting the desired operatingvoltage value on output 91 and provides a second reference voltage thatis used for disabling transistor 14.

Operating voltage detector 39 controls transistor 15 to charge capacitor49 until the voltage on output 91 reaches the desired operating voltagevalue. When the input voltage applied to input 22 is initially appliedto circuit 90, capacitor 49 is discharged. The input voltage increasessufficiently to turn-on transistor 13 and supply bias currents throughresistor 18 to transistor 15. The output of detector 39 starts at a lowvoltage value and remains low until the output voltage on output 91reaches the desired operating voltage value. The low voltage disablestransistor 41 which allows resistor 18 to enable transistor 15 to forman output current to charge capacitor 49 and form the output voltage.When capacitor 49 is charged to the desired operating voltage value, theoutput of detector 39 goes high enabling transistor 41 and disablingtransistor 15 of device 12. The hysteresis of detector 39 functions tokeep the output voltage at the desired operating voltage value asexplained in the description of FIG. 4. Detector 39 has no effect ontransistor 14.

When an ESD event occurs, the ESD charges the gate of transistor 14thereby enabling transistor 14. Transistor 14 is formed to provide adrive current that is sufficient to drive transistor 97 into a lowimpedance state. Transistor 97 typically is a low on-resistance powertransistor that can easily sink currents resulting from an ESD dischargewhen transistor 97 is in a low impedance state. As long as circuit 90 isnot in a normal operating state defined by output 91 greater than thereference input voltage to detector 96, transistor 14 will be enabled bythe high output state of detector 96. Under normal operating states ofcircuit 90, transistor 14 will be disabled thereby allowing a drivercontrol block 98 to control transistor 97.

Those skilled in the art will note that detector 96 may have a varietyof implementations. One example implementation includes a comparator 94that receives the output voltage on an inverting input and the ESDdetection voltage on a non-inverting input. An output of comparator 94is connected to input 23 of device 12.

In view of all of the above, it is evident that a novel device, methodof forming the device, and method of using the device is disclosed.Included, among other features, is inhibiting the operation of a powercontrol system by pulling the output of a startup device to a lowvoltage. The low voltage on the output causes the startup device todisable charging current and inhibits operation of the power controlsystem while dissipating as low a current as possible. Also include isusing one doped region to form the source and drain of a J-FETtransistor and also the drain of two MOS transistors. The single dopedregion is formed as a closed geometric shape. Using one doped region forall three transistors minimizes the cost of the high voltage multipleoutput current device. The closed shape also facilitates forming thesources of the two MOS transistors adjacent to the single doped regionand further minimizing the space utilized for the high voltage multipleoutput current device. The independently controlled MOS transistorsfacilitate using the high voltage multiple output current device for twodifferent currents for sequencing the startup of the power controlcircuit and other circuits requiring multiple independently controlledoutput currents.

It should be noted that element 11 and device 12 can include more thantwo outputs and transistors such as transistors 14 and 15. For example,element 11 and device 12 may include a third transistor in parallel withtransistors 14 and 15. The third transistor could also have a drainconnected to node 16, a source that forms a third output of device 12,and a gate that forms a third input for device 12. The third transistorwould have an associated third resistor having a first terminalconnected to node 16 and a second terminal connected to the gate of thethird transistor. The third transistor can form a third output currentthat is different than the first and second output currents. An exampleof an application using all three transistors could include transistors14 and 15 providing the first and second output currents as explained inthe description of FIG. 4, and the third transistor could provide athird output current to drive transistor 97 as explained in thedescription of FIG. 6. Additionally, element 11 and device 12 may haveany number of such transistors and associated resistors.

1. A power control system inhibition method comprising: generating afirst output current at an output of a system controller responsively toa first value of an output voltage; and coupling the output to a voltagereturn to inhibit generation of the first output current and generatinga second output current at the output while the output is coupled to thevoltage return responsively to a second value of the output voltage thatis less than the first value wherein the second output current is lessthan the first output current.
 2. The method of claim 1 whereingenerating the second output current includes generating both the firstoutput current and the second output current when the output voltage isgreater than the first value, and disabling generating the first outputcurrent and the second output current when the output voltage is atleast equal to a third value wherein the first value is greater than thesecond value, and the third value is greater than both the first valueand the second value.
 3. The power control system inhibition method ofclaim 1 further including receiving an input voltage on an input of thesystem controller, generating the first output current, charging acapacitor coupled to the output with the first output current, anddisabling the first output current when the output voltage is a secondvalue that is greater than the first value.